A novel video recording and playback system has been described by Clemens in U.S. Pat. Nos. 3,842,194 and 3,842,217 incorporated herein by reference. According to this system, video, audio and color information is recorded in the form of geometric variations in a spiral groove on a surface of a disc. Disc replicas, made of an insulating material, such as vinyl, are coated first with a thin, conformal, conductive metal layer as a first electrode of a capacitor, and then with a thin, conformal, dielectric layer. A metal-tipped stylus acts as a second electrode of the capacitor. The stylus monitors changes in capacitance between the stylus and the metal film on the disc as these geometric variations pass beneath the stylus upon rotation of the grooved disc to effect recovery of signals occupying a band width of at least several megahertz, when they are converted back to video, audio and color information suitable for display by a television monitor.
Several metals have been suggested for use as the thin, conductive metal layer. Aluminum was first tried because it is inexpensive, but it was found to be unsatisfactory because it became grainy on storage, leading to high noise levels on playback. Gold was tried and was found to have excellent properties, and is particularly corrosion-resistant, but it is too expensive to use on a large commercial scale. Further, adherence of the dielectric film, particularly glow discharged polymerized styrene, as disclosed in U.S. Pat. No. 3,843,399, to gold surface leaves something to be desired and results in undue wear of the record during playback. Copper was also tried. This metal in thin layers has excellent adherence to polymeric substrates, particularly vinyl compounds, but is not satisfactory because it corrodes rapidly in the atmosphere on storage. Conductive metal alloys of nickel and copper, which are corrosion resistant, have also been tried, but their poor adhesion to organic materials makes them unsuitable for use on the video disc. Thus the search for a thin conductive, adherent, corrosion-resistant metal coating for the video disc has continued.